In aircraft applications, motion is known to be transmitted from an input shaft to an output shaft using a face gear transmission, which comprises two coaxial, counter-rotating face gears positioned facing each other, and at least one floating pinion meshing with both face gears.
In most applications, the face gears are the same size, and the pinion rotates about a respective axis perpendicular to the axes of rotation of the face gears.
Inclined-axis solutions are also known, in which the face gears are again the same size, but the angle between the axis of rotation of the pinion and those of the face gears is other than 90.degree..
Whereas perpendicular-axis solutions pose substantially no problems, inclined-axis solutions, though used, are functionally inefficient and unreliable.
In actual use, in fact, the face gears transmit to the pinion respective actions which, since both face gears are the same size, generate on the pinion a tilting torque acting in the pinion axis plane and which moves the pinion unpredictably with respect to the face gears, thus resulting in an equally unpredictable variation in theoretical torque flow to the two face gears and, consequently, in a variation in stress on the teeth. In particular, a tilting torque on the pinion causes an unpredictable and uncontrollable variation in the specific pressure pattern along the teeth of both the face gears and the pinion, with the generation of localized pressure peaks. Since both the face gears and the pinion must obviously be sized on the basis of maximum possible stress values, the teeth of both the face gears and the pinion are considerably larger than they would be in the absence of said tilting torque, i.e. in a perpendicular-axis arrangement, thus resulting in a considerable increase in weight, size and, hence, cost.